THE REPUBLICAN Party’s dramatic success in the midterm elections and the GOP takeover of the Senate in particular give Republicans both new opportunities and responsibilities in shaping U.S. foreign policy. At the same time, most Republicans in Congress have little or no confidence in Barack Obama’s foreign policy, are offended by his assertiveness in exercising executive power and his occasional outright deception, and are eager for payback. All three of these sentiments are understandable, but Republicans must firmly control the third one—the desire for revenge—in the name of the national interest.

The combination of the president’s constitutional authority and America’s historical practice means that Obama is not only the commander in chief, but also enjoys considerable latitude in running U.S. foreign policy. Yet, taking into account recent polls showing that voters believe Republicans would do a better job than Democrats at managing foreign policy—by a margin of 43 percent to 37 percent—few would be surprised that many Republican legislators want to wrest as much control as possible from the president in this area.

And it is not just a matter of public opinion—attitudes have turned against Obama and his administration in large part due to their poor stewardship of America’s international role. After six years of Obama’s leadership, America is worse off in many key regions. In the Middle East, despite a great investment in American lives, treasure and prestige, the Obama administration is fighting a dispirited rearguard action. U.S. efforts to bolster Iraq against the group calling itself the Islamic State appear too little and too late, while American policy toward Syria borders on incompetence. Likewise, in Afghanistan, American troops are leaving the country with the Taliban largely intact and waiting to launch a counteroffensive—hardly a success story. While the administration has some achievements in its relations with China, tension and suspicion increasingly define our overall ties. Moreover, the administration’s cautious approaches elsewhere have emboldened Beijing in pursuing opportunities to overturn the global and particularly the regional order by reinforcing its narrative of America in decline. In the middle of a major crisis over Ukraine, the administration still rejects the notion of a new cold war and is in denial about the clear and present danger of a military conflict with another major nuclear power. Here, the Obama administration’s denials have as little meaning as its infamous red lines; they are public-relations messages at best.

Nevertheless, Republicans must recognize that Congress is not well equipped to micromanage U.S. foreign policy. Congress has neither the expertise nor the collective sense of responsibility for consequences that is necessary in making major decisions about relations with Iran or Russia. The desire to impose demonstrative punishment on the perpetrators of aggressive actions or domestic repression is not enough to produce results. One clear example is the long-standing congressional temptation to rely on economic sanctions, which may well reflect America’s indignation, but are often counterproductive in forcing other governments to change their conduct in a desirable direction. Moreover, once sanctions are codified into legislation, they cease to function as foreign-policy tools but become permanent parts of the landscape. Witness the Jackson-Vanik amendment, which lived on long after the end of the Cold War.

Congress should investigate, expose and debate Obama’s policies. However, passing resolutions, or even laws, without understanding the potential consequences is irresponsible. For example, some appear to make the dangerous assumption that it would make Ukraine more secure to declare the country a major non-NATO ally (like Israel, Australia or Japan) without making a commensurate commitment to defend Ukraine from Russia. Ukraine is not where the West wants to confront Russia militarily. Russia is not the Soviet Union, but geography gives Moscow a huge tactical advantage in both conventional and shorter-range nuclear forces. No less important, Moscow views Ukraine’s future as a vital interest—meaning that we should not ignore the possibility that Russia could take a stand against all odds. The combination of lethal U.S. military assistance, declarations that Ukraine is an ally and Ukraine’s NATO aspirations could well trigger a preemptive, large-scale Russian invasion. At that point, not only Ukraine but also NATO’s overall credibility and America’s fundamental national-security interests would be at stake. Republicans in Congress should think carefully before attempting to enter such dangerous waters, especially when they are the first to question President Obama’s ability to act as a true national-security leader.

THERE ARE, however, a number of important things that the new Republican majority can and should do to enhance U.S. national security and American international leadership.

1. Put an end to sequestration and increase the defense budget above the Obama administration’s requests. Increases should be smart and carefully targeted, with no pork and no wasteful spending on nonexistent problems. The clear goals should be to improve U.S. military capabilities and to send a Reaganesque message to U.S. friends and foes alike that nobody should mess with America—and nobody can win an arms race with it.